Since an ink jet recording system produces no noise, requires neither developing nor fixing process, and can make not only high speed recording but also multicolor recording very easily, it is rapidly coming in wide use in facsimile, word processor, terminal printer, etc., in recent years. Above all, the development of the color printer based on the ink jet recording system which prepares color hard copy from color display is being progressed. As the ink jet color printer there have been developed color printers of high resolution which can be used not only in the field of color graphics using seven representing colors (yellow, magenta, cyan, red, green, purple, black) but also recently in the so-called pictorial color copy, that is, full color copy which can provide images of high image quality close to gravure printing or silver salt photograph.
The ink jet recording is advantageous in that ordinary plain paper, the so-called plain paper copies (PPC) can be used. However, it is the real situation that in general the ordinary plain paper cannot satisfy the requirement as the ink jet recording paper adapted for multicolor recording.
The fundamental properties required for the ink jet recording sheet may be enumerated as follows.
1. The shape of the dot is circular without spreading in blots, and the periphery of the dot is sharp having high resolution.
2. The dot is high in color density and good in sharpness.
3. The absorption velocity of ink is fast, the dryness is excellent, the amount of the ink absorbed is large, and moreover, when the dots of ink overlap each other, the dot later adhering does not run, and so on, thus proving to be well suited to multicolor recording property.
4. After recording, dimentional variation is small, and curling, waving, and deformation are not found, and so on.
Above all, it is now becoming a technical subject among those skilled in the art to make compatible the mutually contradictory properties, i.e., the absorptiveness against ink that governs the dryness of ink and the property of spreading (blot) of the dot.
Namely, when the absorptiveness against ink of the recording paper is fast, the spreading of the dot is enlarged and the shape of the dot is also distorted, so that the resolution is aggravated. Furthermore, the ink has a tendency to penetrate into the paper layers so deeply that both the color density and the sharpness are lowered.
Besides the above, where high image quality is to be obtained by the recent multicolor recording, the inks of the respective colors adhere to the same place or its neighborhood on the recording sheet in a short period of time, so that particularly a large absorptive capacity against these inks is requested along with the absorptiveness against these inks. Otherwise, the unabsorbed inks may run out (flow), and as the result no sharp image may be obtained as well as stain may be caused to generate.
As the ink jet recording paper the ordinary plain paper such as fine paper can be basically used, but it is the real situation that those skilled in the art of manufacturing the recording paper adapt various paper properties such as the degree of sizing, air permeability, density, smoothness, and dimensional stability such as elongation in water, etc., to the recording system, or the conditions or the ink thereof. On the other hand, in order to obtain the color recording of high image quality that is the recent tendency, even by controlling all the above described physical properties it is not possible to achieve the object in doing so alone. Therefore, in order to acquire the recording characteristics satisfying the above described fundamental requirement it is now under investigation to obtain an ink jet recording paper of coated paper type in which the pigment, binder, etc., have been made optimum by providing a coated layer on the surface of the sheet. Nevertheless, in actuality that is found as yet no ink jet recording paper for high image quality use, which can satisfy, not to mention the recording performance, every point of the water resistance, weather resistance, dimensional stability, etc., of the recording part. Recently, there is a tendency that it is requested to use as the substrate sheet not only paper but also either water-proof sheet or transparent sheet such as impregnated paper, plastic film, synthetic paper, metal sheet, etc. For instance, concretely as the color display introduction into a personal computor progresses there is requested transparent film which is capable of ink jet recording for use of color hard copy in overhead projector (OHP). However, the plastic film such as polyester, or the like, used in OHP cannot be used since it is entirely lacking the absorbency to aqueous ink due to the hydrophobicity differing from paper substrate material. The other processed papers such as impregnated paper, etc., synthetic paper, metal sheet, etc., are also the same as above.
In the development of the ink jet recording sheet using as the substrate material such a novel raw material it was found that so far as we are at grips with this problem based on the conventional concept concerning the manufacture of ordinary plain paper or coated paper there should be a technical limitation.
Still further, as the solvent of an ink used in ink jet process water cannot be used alone because the jetting nozzle is clogged by the evaporation of the water, so that, in order to avoid such clogging due to drying there are various devices such that polyalkyleneglycol or other wetting agents are added to water. However, when recording on the recording sheet made of synthetic resin film, or the like, by the use of such an ink and solvent, this reversely results in aggravation of the dryness of the ink.
As above described how distinctly and sharply the ink dots by ink jetting can be made to adhere and moreover how rapidly they can be made to be absorbed and dried on the recording sheet particularly on the transparent synthetic resin film such as polyester, etc., are the most important problems in the field concerned.